Soot-removal blowers are employed to blast soot off heat-emitting surfaces in boilers and heat exchangers for example. They are charged with a fluid, air or steam for instance, at an elevated pressure that is reduced in their nozzles to the level prevailing in the heat exchanger. The jets leaving the nozzles accordingly have enough kinetic energy to remove undesirable deposits from the inner surface of the heat exchanger.
The cleaning efficiency of a soot-removal blower depends on the size of the nozzles and from the level of pressure at which the gaseous fluid flows into them. More fluid per unit of time can flow through a nozzle and more soot can be dislodged when the fluid is more highly compressed and when the nozzle has a longer diameter.
Although the pressure in the intake line is generally substantially higher, 40 to 60 bars for example, the fluid usually enters the nozzles at a pressure of 3 to 20 bars. In known soot-removal blowers the pressure is reduced to the level needed for cleaning by a variable choke disk accommodated in a valve. From the valve the fluid flows to the nozzles through such other design-dictated components as a core and a lance. To ensure that the soot-removal blower will clean as effectively as possible, as much fluid as possible must flow to the nozzles. In this context, however, the high flow rates that occur in the sections downstream of the soot-removal blower are detrimental in that they lead to severe pressure losses and to more noise. Once permissible noise levels are exceeded, expensive noise-insulation cladding is necessary or the level of fluid per blower must be decreased, meaning that more blowers must be added to the boiler or heat exchanger. Either approach substantially increases the cost of the cleaning system.